290 MINNESOTA BOTANICAL STUDIES 



oryzoides are common members of this association as it is seen in 

 linear form near streams. Some of the species that have already 

 been noted for the marsh are more or less common as straggling 

 communities in this association. Thus Scirpus validiis, S. ameri- 

 canus, Phragmites, and Typha are all frequently seen as tufts or 

 narrow patches either in pure or mixed stands along all of the 

 streams of the region. Numerous additional sedges become locally 

 abundant. Tufted species of Carex such as C. gravida, C. festu- 

 cacea, C. stipata, and C. hystricina, are especially common in such 

 places. 



The Meadow Formation 



The earliest aspect of the meadow formation is seen in the form 

 of a wet meadow, as a rule closely following the bulrush-reed-grass 

 association of the previous formation. Occasionally the smartweed 

 association or the streamside marsh variations lie between the 

 meadow and the more aquatic associations. The wet meadow is usu- 

 ally intermediate in position and development between marshes and 

 meadows proper. Where, as along streams, the marsh formation 

 is developed in the form of straggling bits or in narrow marginal 

 belts, this formation is often conspicuous as alternating patches that 

 occupy slightly higher levels but still with a soil that is very wet 

 and soggy for the most of the season. 



The lowest of the meadow associations, namely the rush-sedge 

 wet meadow association, because of a slightly more elevated position 

 occupies a sandy substratum with a much lower soil-moisture con- 

 tent than is characteristic of the marsh, although during wet seasons 

 this difference becomes much less. Quite naturally this and the 

 previous formation are not separated by a definite boundary line, but 

 because of a very gradual change in edaphic conditions a transition 

 belt is usually noted within which the one formation loses its identity 

 and the other makes its appearance. Such belted transition areas 

 are frequently of considerable breadth and their floristic character 

 partakes of the typically developed formations lying on either side. 

 On the other hand a more abrupt change is brought about where the 

 pond or lake is bordered by a distinct bank a few feet in height. 

 Under such circumstances the wet meadow species may be totally 

 absent, while the other meadow forms approach the edge of the low 

 rim which constitutes at the same time the outer boundary of the 

 marsh formation. Abrupt topographic transitions are thus seen 



